The present invention relates to a switching device for opening and closing a load circuit, in particular in an electric vehicle, having at least one switch contact which can be moved from an open position into a closed position and which is held at a distance from a counter-contact in the open position and is in electrically conductive abutment with the counter-contact in the closed position.
The invention further relates to a method for switching a load circuit, in particular in an electric vehicle, at least one switch contact being moved from an open position into a closed position and thereby being brought into electrically conductive contact with a counter-contact.
Switching devices and methods of the above-mentioned type for switching load circuits are known from the prior art. They are used for repeated switching, for example, in order to be able to separate a battery or an accumulator of an electric vehicle from consumers when they are not in use, or to be able to open the load circuit. The switching devices are consequently generally contactors.
In addition to the contactors, it is necessary to protect load circuits from overload. In particular in electric vehicles, owing to a relatively low internal resistance of the batteries or the accumulators, very high short-circuit currents may occur in the event of the malfunction of a component and in particular involve the risk of fire and are therefore intended to be prevented. Thus, a regular maximum load current may, for example, be up to 200 A, whereas a short-circuit current at from 2000 to 6000 A can exceed the load current by more than ten times.
In order to protect load circuits from short-circuit currents, there are used, for example, in electric vehicles, fuses which, owing to the large tolerance range thereof, can be used only as a back-up fuse. Back-up fuses, for example, in the form of melting fuses, can continuously guide currents at least up to a rated current. When the rated current is greatly exceeded for a specific period of time, it causes a fuse element of the fuse to melt, whereby the load circuit is interrupted and the fuse becomes unusable. The activated and consequently unusable or “burnt-out” fuse must be replaced.
However, the back-up fuses can generally interrupt a load circuit only at currents above a specific multiple of the rated current thereof until a rated breaking current is reached. Consequently, normal fuses cannot be used in a reliable manner in the event of excess currents which are between the rated current strength and the said multiple of the rated current strength up to the rated breaking current.
In the region between the rated current and the multiple of the rated current strength up to the rated breaking current, in which excess currents, for example, of up to approximately 30% of the short-circuit current may occur, it is therefore necessary to use more powerful power contactors which, in the case of electric vehicles, are accommodated, for example, together with the fuse, in a battery separation unit. However, the simultaneous use of fuses and more powerful power contactors increases the mass and costs of the battery units.
Alternatively, line protection switches can be used to separate the battery from the consumers or, in the case of electric vehicles, from the on-board power supply. Owing to the use of the line protection switches and the fuse function which they perform, it is again possible to use lighter and cheaper switching devices for regular switching operations. However, financial expenditure and complexity in terms of weight when line protection switches are used to interrupt short-circuit currents in electric vehicles are currently considerable. For instance, the line protection switches contain an electromechanically activated actuation mechanism and furthermore generally means for extinguishing electric arcs, such as, for example, quenching plates, magnets, blow-out coils and/or hermetically sealed chambers with pressurised gas. Compared with melting fuses, line protection switches at least have the advantage that they are designed for multiple short-circuit current interruption, and consequently can be reset after activation and do not have to be replaced owing to unusability.